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How can I find the maximum climb angle of a propeller driven aircraft from a graph of vertical velocity against airspeed?
I've been asked to find the maximum climb angle of a propeller driven aircraft from the graph of vertical velocity against airspeed:

How can I do that?

Does this answer help you?

Can you post the graph?

I just noticed that your graph already includes the origin (0,0). Using the approach described in my answer, you can come up with the answer in less than a minute.  No re-plotting is needed.

Tangent from 0, 0 to the curve yields point of max climb angle (maximum height for least distance traveled). Highest point on the curve yields maximum climb rate (obviously).

Interesting airplane; looks like Vy is more than double Vx! (More characteristic of a jet with a high thrust loading -- see diagram on this answer -- http://aviation.stackexchange.com/a/22299/34686 ). Of course it's surely a made-up curve, but just saying...

All you need to do is to plot vertical versus horizontal speed using the same scale on both axes. Then the solution is the point with the steepest angle from the origin of the graph.
Of course, it helps to do this in metric units. And to add a description to the axes of a plot. The solution can then be directly read from the graph.

@quietflyer: Yes, this requires another arithmetical operation because airspeed is the vector sum of vertical and horizontal speed. Any spreadsheet will be able to do this.

"Of course, it helps to do this in metric units."-- why?

@quietflyer It does not matter as long as the units are the same. With metric units for speed (meters per second), this is the case. With imperial units, we typically use different units for horizontal speed (knots, i.e. nautical miles per hour) and vertical speed (feet per minute).

This is a nice concise answer with a nice graphic.  But unless the data is already loaded up into a spreadsheet ready for re-plotting to a new scale, there's a much faster way to solve the problem.

Of course when someone metricly assumes that one is both climbing and flying forward in m/s, that must be some airplane!
To truly be expert, one must confirm the units of climb and airspeed. Spreadsheets are indeed are helpful here, and may be programmed as follows:

Same units of Velocity for climb and airspeed. (meters/second)

Conversion of airspeed to horizontal velocity:
Arc Sine ratio of Vv/Airspeed = climb angle
Cosine of Climb Angle x Airspeed = Horizontal Velocity

For low angles of climb (non high performance aircraft) airspeed may be directly compared to vertical velocity, as the cosine of lower angles is very close to 1.
Plotting it as Peter Kampf did yields the airspeed of maximum climb angle.  From the spreadsheet, this climb angle can be read.

Just as an aside, the vertical speed can't be higher than the airspeed, so it's not even theoretically possible that the units could be the same on both axes of the graph in the original question-- but if the lower axis were horizontal speed it would be possible, and yes that would be quite some performance!

Assuming no wind--
The steepest climb angle occurs when the ratio of vertical speed to horizontal speed is maximized.
In many aircraft the difference between horizontal speed and airspeed will be trivial.  But even in high-performance aircraft capable of steep climb angles where this is no longer the case, it can be geometrically shown that the steepest climb angle also occurs when the ratio of vertical speed to airspeed is maximized.  Both approaches are minimizing the same angle on the right triangle comprised of the vertical speed, horizontal speed, and airspeed vectors.  And both approaches are maximizing the same angle on the right triangle comprised of the vertical speed, horizontal speed, and airspeed vectors.  Therefore both approaches must have the same solution: when the ratio of vertical speed to airspeed is maximized, then the ratio of vertical speed to horizontal speed is also maximized.  So your graph of vertical speed versus airspeed will work just fine for finding the maximum climb angle.
One way to find the maximum ratio of y to x on any graph of y versus x is to extend the axes of the graph to include the origin (0,0) and just run a line from the origin to any point on the curve and find the point on the curve where the slope of this line is the steepest, just as was done in these related answers: What is the typical climb angle (versus the ground) of a single engine piston plane? , Does an airfoil drag coefficient takes parasite drag into account? .  Note that the line from the origin will have the steepest slope when it is tangent to the curve on the graph.  Note also that the units of the graph need not be the same on each axis for this method to work.  So no re-plotting is needed, just get out your ruler and start drawing.  Since your graph already shows the origin (0,0), you are almost done already!
Once you know the data point where the climb angle is maximized, you can find the actual climb angle with a bit of trigonometry involving the right triangle comprised of the airspeed, horizontal speed, and vertical speed vectors.  You don't have to know all three of these values-- any two are sufficient, and in this case you'll know the airspeed and the vertical speed.  The climb angle will be the arcsine of (vertical speed / airspeed).  Naturally, for this calculation you'll need to use the same units for both values-- a conversion may be necessary.
While you are at it, just the sake of curiosity you might want to also calculate the arctangent of (vertical speed / airspeed) for the same data point.  That's the actual angle of the slope of the straight line you drew on the graph.  If the two values are almost the same, that indicates that the airspeed and horizontal speed are so close as to be practically interchangeable, at least at that point on the performance curve. (As a point of trivia, it looks like if the horizontal units on your graph are knots and the vertical units are feet/min, then the angle computed with the arcsine is about 4% larger, or about 0.6 degrees larger, than the angle computed with the arctangent.)
Note that with a curve shaped like the one you've included in the question, the precision of your final answer is not going to be extremely sensitive to how well you are able to determine the exact point where the line from the origin is tangent to the graph.  In other words if you vary the point of contact between the line and the curve slightly, the resulting climb angle will barely change at all.  Note also that the data point you use for your trig calculation of climb angle can come from anywhere along the straight line you've drawn from the origin of the graph.  You need not use the actual point where the straight line touches the curve.  For example you can choose a point where the straight line crosses one of the airspeed or vertical speed indices, or where it crosses an intersection of both airspeed and vertical speed indices.
Or, if you've re-plotted your graph with the same scale on each axis, and you aren't worried about the difference between airspeed and horizontal speed, you can forgo the trig calculation and just use a protractor to measure the angle between the tangent line and the x axis of your graph of vertical speed versus airspeed. It's going to be harder to get a precise answer this way, and it may end up taking you longer.  Since you've already shown us a perfectly good graph of vertical speed versus airspeed, you might as well use it via the method described here.  You should be able to come up with the answer in less time than it took you to read this!

Don't let the length of this answer fool you, it is actually the fastest path to a solution, starting from what we're given to work with in the original question.


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Can line and light maintenance be combined?
Is there any possibility to combine line maintenance and light maintenance (containing A, B and C check) under the name of line and light maintenance? In real is there any company which possesses a line maintenance which carried out "A" check and so on?

you should add a country, Im not an ame but in Canada operators can get there own maintenance scheduled approved by Transport Canada. I have know idea any of the details.

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What is the difference between mist and haze in terms of relative humidity?
I am an aviation meteorologist and I struggle to distinguish the two of them.

If you are an aviation meteorologist surely you would know...

Welcome to aviation.SE! Since this seems to be a general weather question, you might get a better response on earthscience.SE.

If you happened to live where I do, you would readily appreciate the difference.  Relative humidity is currently 26%, visibility at the nearest commercial airport is 4 miles in haze (from numerous wildfires): https://www.flightstats.com/v2/airport-conditions/RNO

The term haze does not say anything about the humidity of the air because it is by definition caused by dry particles, so not by water. If you have mist (or fog), then water droplets are suspended in the air, which usually comes with 100% humidity.
Here is a set of definitions by the UK's Met Office:

Fog
In our meteorological glossary fog is defined as 'obscurity in the surface layers of the atmosphere, which is caused by a suspension of water droplets'.
By international agreement (particularly for aviation purposes) fog is the name given to resulting visibility less than 1 km. However, in forecasts for the public, this generally refers to visibility less than 180 m.
Mist
Mist is defined as 'when there is such obscurity and the associated visibility is equal to or exceeds 1000 m.' Like fog, mist is still the result of the suspension of water droplets, but simply at a lower density.
Mist typically is quicker to dissipate and can rapidly disappear with even slight winds, it's also what you see when you can see your breath on a cold day.
Haze
A third term you might also hear mentioned is haze. This is a slightly different phenomenon which is a suspension of extremely small, dry particles in the air, not water droplets. These particles are invisible to the naked eye, but sufficient to give the air an opalescent appearance.

(metoffice.gov.uk)
Also see: What is the difference between mist and fog?

Thanks for your answer

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Where can I place an engine in a twist morphing wing?
I am designing an electric aircraft with a wing that is completely based on the idea of biomimicry, whereas the wing has multiple winglets and can also morph by twisting. It is more like an experiment to check about the possibilities of a commercial aircraft with the ability to morph.
Where could I possibly place the engine if my wing is going to be able to twist?

I don't want to be on the nose about it, but how about on the nose? :)

Don't
Twist, morphing sounds torsionally flexible. Add mass to a soft spring and you get all kinds of resonances and eigenmodes. Better put the engine mass to a stiff and strong structure that can deal with its mass and forces.

I suppose one could implement digital augmented damping, similar to the fly-by-wire damping of phugoid aerodynamic oscillations. But, as the pioneers discovered, as soon as you start flying at any speed, the warp control forces become horrendous. One of them described it as the controls flying the pilot.

@GuyInchbald I agree, and then it remains to be proven that the benefits of the warping wing with all additional controls and the redundancy this requires added will still exist.

Maybe within the wing towards the root, like in the concept of the Eather One (or de Havilland Comet).
Otherwise, if it's a X-57-like concept, with distributed electric propulsion, I don't see why it couldn't work.
Feather-tipped wings have made their way to Airbus' Bird of Prey conceptual proposal, although I don't know if that's the kind of biomimicry you refer to.
I'm also not sure whether there was a lot of technology maturity/consolidation from the flight testing campaign using a Gulfstream with morphing wings.

Distributed propulsion with twisting would likely lead to distributed thrust vectors and unpredictable vibration modes. I would not recommend it here.

The Wright brothers offset the engine to one side and the pilot to the other. The engine drove twin pusher props via bicycle chains. Outboard of that rigid centre section, control was by wing warping. Don't knock it, the plane flew on only 12 hp. But maybe you could improve on the bicycle chains.
Another approach is to place the engines at the tail. In the 1960s and 70s airliners such as the Sud Aviation Caravelle and BAC One-Eleven and Trident were quite successful, and a lot of bizjets have them tail-mounted too.

The Caravelle is from the Fifties (first flight 1955) and all tail-engined airliners are from the early to mid-Sixties. The last one was the Tu-154 (first flight 1968). After that the designers had learnt their lesson.

@PeterKämpf The Caravelle did not enter service until 1959. But I'll grant you the swinging sixties. How good an idea is and how successful are not the same thing, and neither is the same as how possible it is.

Once the difficulties of wing aerodynamics with an engine attached are solved, the wing mounted engine really is the better solution. For a multitude of reasons. But the wing should not be wobbly.


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How could an airliner as big as B777 make a U Turn on ground?
I just heard about this 4 month old incident, where a United Airlines B777 made a U-turn, while it was on way to runway. What is the turning radius required to make such a U-Turn? Also, is so much space available near the taxi area at the IGI Airport? At last, is this a common practice for airliners to do?

The Daily Mail is a notoriously sensational, inaccurate newspaper and in this case I think the term "U-turn" is used figuratively, not literally: the aircraft simply returned to the gate and the artwork even shows it following a semi-circular taxiway. On the other hand, your question about the turning radius is a good one.

As can be seen on the IGI airport diagram, there is plenty of space where an airliner could "turn around" and head back to the gate. Worst case, they would roll to the runway, and instead of starting, just roll down the runway to the next "exit".

From looking at aerial photos of Kjevik airport, Kristiansand, Norway, I can confirm that a 737-class airliner needs no more than a 60m circle of tarmac for a U-turn.

@Pondlife I have observed the taxiway of IGI several times, through the windows but never really observed any semi-circular pathway..

The picture in the article is an illustration, it isn't reality. My point is simply that "U-turn" only means that the aircraft returned to the gate. It doesn't mean that it literally turned around in the taxiway. The article is taking an unusual but not inexplicable event and turning it into a 'drama' with hints of conspiracy theory. This is entertainment, not a factual, accurate news report.

@Pondlife as you already pointed out, U-turn is not return to gate. U-Turn is U-turn and return to gate is return to gate. It's just that Daily Mail is inaccurate, to the point that one may call its articles misleading.

The article says nothing about it being a 777; the photograph is a 747. What's your source for the kind of plane?

@DavidRicherby as said above, Daily mail is a notoriously reported mail.. See this

Related: here's a video of a British Airways Airbus A318 doing a U-turn on the runway at London City: https://www.youtube.com/watch?v=noAyUIk89AU

Turning Radius, as found in a planning document:

28.7m for a Boeing 777-200
34.7m for a Boeing 777-300

Rotating around one a point a bit off the wing to allow both wheels to roll throughout.
Minimum Pavement Width

47.5m for a Boeing 777-200
56.0m for a Boeing 777-300

Source
Be aware that this is not exactly ideal- visibility from the flightdeck is not great and you do not want the gear running into the grass or edge lights. An Emirates A380 screwed up in Warsaw not too long ago when trying to pull this stunt.
Since this width is not normally provided by the runway (even Heathrow only has 45m and 50m runway width), you will add turning pads at the end unless there are taxiways you can use instead.

Source

Or to explain they pivot around one of the main gear.

@ratchetfreak it doesn't quite pivot around the main gear, but it's close.

I would imagine pivoting on a single wheel would mar the pivoting tire, so it must roll at least a little.

@corsiKa: Right, and the 777 has a 6-wheel dolly. Pivoting around one tire would not be possible - the forward and rear ones would need to move sideways at full load.

@MikeFoxtrot just waiting for you to answer is this a common practice for airliners to do?

@anshabhi Doing a 180 degree turn on a runway is a regular occurrence at some airports. For example, take a look at the taxi diagram on page 10-9 of http://uvairlines.com/admin/resources/charts/SAEZ.pdf for Ezeiza International at Buenos Aires. If you're landing on rwy 17 and roll past the intersection with rwy 11/29 you have to do a 180 on the runway as there is no parallel taxiway. There is a turnaround at the end of rwy 17, but if you're down to taxi speed just past the intersection, there's no point in wasting the time and fuel to taxi to the end. At least I never did.

The longest 777 s have  steerable wheels on the mains and also a GMCS (ground cam showing the wheels) to assist pilot. If you want to make the smallest turn with an aircraft you have to use differential braking and asymmetrical thrust: Press hard on the toe brake on the side you want to turn, tiller full deflection and increase thrust on the opposite side. However this is some stress on the tyres and landing gear.
Data are available on that link, section 4.2 http://www.boeing.com/assets/pdf/commercial/airports/acaps/777_2lr3er.pdf

The aft two wheels on the mains are steerable on a a 777 but are limited in their turn radius and do not engage unless the commanded turn is pretty sharp, as I recall from my days at Everett.

Theoretically it is possible to make a pivot turn on a B777, according to the Flight Crew Training Manual (FCTM) from Boeing.
Such a turn is started after lining up with the edge of the runway, stopping the aircraft completely,locking the brakes on the inner side of the turn and applying thrust to the outer engine on the turn. The wheels on the inner side of the turn will be really locked and subject to a high stress, and there is potential for tyre and runway surface damage. Such a turn on a B777-300 would require a minimum runway width of 43.6 meters.
It is a procedure that involves ground crew coordination and supervision and quite a risk both for the personnel involved, the landing gear and tyres and the runway surface, so it is not a normal manoeuvre, probably used only in an emergency situation where no other option is available. Having a tug to manoeuvre the aircraft around could be a much better option.

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Why was Concorde's cockpit so complex?

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Why was this cockpit much more complex than any other modern day aircraft or a fighter jet? It looks to have many more buttons and controls, and very small (interesting) screens. Also, its steering was much different than you would see in any other aircraft.

related, if not duplicate: http://aviation.stackexchange.com/questions/2873

It's not modern!  It's 60's technology, much of it designed in the 50s.  Not much different to any other complex aircraft of the time.  In what way do you mean "the steering is different"?  It also has no "screens".  Do you mean the coloured instruments in front of the pilots?

possible duplicate of Why are the cockpit controls of airplanes so complicated?

@DavidRicherby it's "related, but not duplicate". See, this received only one close vote.

Half of the buttons are to control the nose ;-)

As a former 747-100/200 pilot, its complexity doesn't look at all abnormal.

It was not complex! It was very cluttered, but in essence it was very simple—every element did just one thing. That's what “simple” means—its elements do one thing each, independently. Modern cockpits are vastly more complex. They have multi-purpose elements that do many things depending on modes and context. That's what “complex” means—doing things that depend on each other in non-trivial ways. The complexity is more manageable in this case though as through clever design only the relevant complexity is shown at any moment.

......Because it was designed in the 1960s when we still filled the cavities in our teeth with mercury and made black people sit in the back of the bus.  Whole lotta things change in 60 years or so.

Why was this cockpit much more complex than any other modern day aircraft

Firstly, as others have noted, you imply Concorde was modern when you compare it with "other modern" aircraft. OK, it was a "jet-age" aircraft, but it wasn't a 21st Century design. it was designed before "glass cockpits" were possible, in the 1960s. There were no real multifunctional displays then, so there had to be a switch or dial for every possible action and every possible parameter the pilots might need to know about.
The main difference is probably the flight engineer's panel on the right. Modern aircraft have two pilots in the cockpit and no flight engineer. I imagine that increased automation in engine controls mean that the engine management by the crew is much simpler and requires fewer controls and dials. These are now typically located in the center of the main instrument panel above the thrust levers etc.
For comparison, here's (a somewhat poorly stitched panorama of) a 747 cockpit

Image by Eric Long, National Air and Space Museum, Smithsonian Institution
and a rather better photo of a 747-300 cockpit (though lower central controls are obscured) ...

Image © aroosh

or a fighter jet?

A lot of the controls and instruments are duplicated in a two-pilot cockpit. In a fighter jet, you only see one set of instruments and controls. Also a one-engine plane will have a quarter the engine controls of a four engine plane. Fighters probably lack an APU.
Although fighters have additional switches etc for armaments, airliners have additional switches etc for passenger related facilities (seatbelt lights, a/c? etc), security (cockpit door), cabin-crew comms and so on. They also may have more fuel tanks and maybe more means to move fuel around in flight to trim the aircraft.

It looks to have much more buttons and controls,

Modern glass cockpits just hide all that complexity, just imagine you could rotate 90% of what you see out of view.

and very small(interesting) screens.

There are no screens at all. There is a colourful moderately-complex artificial horizon instrument which also shows aircraft attitude and a few other things. The visual part is essentially mechanical rather than created by a light-emitting digital display.

Also, its steering was much different than you would see in any other aircraft.

The shape of the control yoke may be slightly unusual but it operates the same was as any more common yoke design. You push it forward and back to control the pitch using the elevator (or elevons) and you rotate the top part left or right to control roll using ailerons (or equivalent control surfaces). There are buttons on the had grips to control a few functions. I think the shape was partly to make it easier to get in and out of the seat.
Heres a similar yoke design in an Embraer ERJ-145LR

Image © Micheal Catchpole

This style of 'yoke' give more legroom, especially when getting in/out of the seat.

As others already said, the keyword in your post is "modern" and Concorde is not one. You compare dissimilar things. Try comparing with something similar, a Boeing 747-200 cockpit for example:

Copyright owner: Achim Pfennig
Now compare the pictures. You will notice the same level of complexity in the cockpits. Sure there will be differences if you make an in-depth research, but bottom line is that analogue cockpits look "cluttered" compared to the modern and "sleek" glass cockpits.

Why was this cockpit much more complex than any other modern day aircraft or a fighter jet. It looks to have much more buttons and controls, and very small(interesting) screens

The cockpit is much more complex than any other modern day aircraft or a fighter jet because it is an Analogue cockpit. Concorde was designed in the 60's and at that point of time the technology was not simply advanced enough to have LCD screens in the cockpit, and neither capacitive/resistive touchscreens were around the block. Hence this left switches/levers as the only options with the designers and that is why you see a lot of these in the cockpit.
Additionally, Concorde had a lot of additional controls like the Droop Nose and the Afterburners for supersonic flight. Such additional controls would need more switches, and increase the complexity of the cabin.
Also, since the on board computers were not very advanced at that point of time (even though Concorde had one of the most intelligent computers at the time of its inception), hence the flight engineer and the cabin crew had to monitor and control a lot of systems manually, and since the cabin was very cramped (as can be seen in the image), this gave a very claustrophobic and complex look to the cabin.

Concorde first flew in 1969.  The initial designs started in the 50s and most of the technology is no older than mid-60s.

Editted the answer. Thanx :)

Concorde was different from other aircraft simply because its design origin lies in the technology of the 50s and 60s and it was designed to do something very different from subsonic aircraft. Namely to fly 100 plus people in comfort above mach 2. Some extras required to achieve this included: 11 fuel tanks with controls to ship fuel around to trim the aircraft in flight, with someone to manage that task. A skin and window cooling system because it got hot and without it would burn anyone touching a window. Engine air intake controls because engines cannot accept air at mach 2. Adjustable jet pipes to optimise engine performance. The droop nose because it needed to be streamlined in cruise but the pilots needed to view the runway on landing and taxiing. Reheat controls for oomph. And I guess a few other things as well. So you can't really compare Concorde with any other current subsonic aircraft. We need a new modern supersonic equivalent with which to compare. The flight deck will obviously have a more modern look but the the physics of supersonic flight still need to be managed.

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Can a commercial airliner be used for military purposes?
Is it possible that in case of some very serious emergency, a commercial airliner such as the B777F could be used for dropping bombs or to serve some other fighting purpose?
 I am simply asking about this from a technical standpoint.

Refitting them for combats would probably be too expensive, not to mention that most passenger jets are owned by commercial airliners, which wouldn't take it too lightly the governments taking their most important and expensive assets to risk them being shot down. But they can surely be used to transport troops and supplies. Or you can do the 9/11 thing. The most practical reason why it would never happen though, is that if passenger jets are often used for military purpose, it might get the enemy to start shooting innocent passenger jets.

There are also some "hybrid" variants, such as the Airbus A330MRTT, that can be relatively easily refitted for another purpose. A330 MRTT can be used for civil flights and, if needed, modified to a tanker.

I don't even know any AWAC that are fitted to also be a fighter.

I read somewhere that significant portions of the resupply lines during the 2003-2011 Iraq war were outsourced to private logistics providers. (Not within Iraq, but from the US to the staging areas outside of the borders.) IOW: munitions, supplies, etc. were literally fedexed to war. Does that count? After all, FedEx (and others) used their own commercial planes to fly supply missions for a war under a military contract.

I'll have to dig to find the reference, but I'm positive this (drpping bombs from a cargo plane) actually happened in Africa.

@MSalters The USAF launched an ICBM from a cargo plane (a C-5, of course.) https://www.youtube.com/watch?v=96A0wb1Ov9k

@LieRyan Most passenger jets are not owned by "commercial airliners." Or even airlines. They are owned by leasing companies. Commercial aircraft are leased for military work all the time. It is extremely common. But using them as a weapons delivery platform is a different story.

@Sami not an AWACS, but the British Nimrod MPAs (which were closely related to their Nimrod EAW variant) were fitted with AIM-9 Sidewinder air to air missiles after the Falklands war. I believe their Shackleton EAW aircraft I believe also retained some of their gun turrets from when they were bombers.

Retrofitting is (as the comments to your post have already stated) rather difficult and unusual. In addition, the quality of service from such an aircraft you could expect to get would most probably not be great. Analogy: Try changing your minibus for 9 people into minivan for freight and industrial work.
It is also worth mentioning that the difference in operation is substantial between bombers and commercial jets. You would be better off using something that is not that complicated, like a Cessna Caravan for instance.
I think that energy, time and money would be better spent on building more dedicated aircraft. Changing the commercial ones is also not trivial and will require engineered changes.

It is however fully possible to design a military derivative of a commercial jet. The Boeing P-8 Poseidon is an example of this, being based off the Boeing 737 with the necessary modifications.
The armament is also fairly extensive:

5 internal and 6 external stations for AGM-84H/K SLAM-ER, AGM-84 Harpoon, Mark 54 torpedo, missiles, mines, torpedoes, bombs, and a High Altitude Anti-Submarine Warfare Weapon system[

Converting pretty much any passenger hauler into a bomber would be quite an exercise. You would have to add pressure bulkheads aft of the flight deck, rebuild the bottom of the fuselage to allow for doors, add considerable structure to hold the (very heavy) bomb racks, and probably remove the floor - rather tricky if the floor is also holding the fuselage together.
Missiles on the wings would be comparatively easy - they are not as heavy and don't require major mods to the pressure hull.
A "serious emergency" indicates urgency, and that gets met with existing aircraft. The time taken to modify a 777 into a bomber would be fairly close to building a new bomber. Although if it's a protracted war of attrition* I would expect Boeing would quickly design a new one based around the 777's tooling so they can get them out the door quickly.
It is very easy (and common) to use passenger haulers as troop transport. Conversion to AWACS is nowhere near as complex, I suspect someone already has plans in a file somewhere to do just that. And the USAF already uses DC-10 freighters as tankers - the boom is a not-overly-complex conversion and probe-drogue systems are almost bolt-ons.
Before anyone comments about it, the DC-10 used as a water bomber is very different from dropping explosives. Water is a distributed load, and releasing it doesn't require half of the bottom of the plane to open up - it flows out through ports that can easily have structural members running across them.
* World War II would be a good example. Evenly-matched belligerents, whoever has more resources usually wins. If WWIII goes nuclear it will be over in an hour or two.

Could the DC-10 water bomber be fitted with liquid napalm?

@collector Probably, along with any number of biological agents carried by liquids.  In fact there's probably a long list of extremely dangerous liquids that could be used if a country really got that desperate.

The A330 is probably the best-suited airliner for an emergency tanker conversion.  It uses the same wings as the A340, simply leaving the outer engine hardpoints unused -- this means that they're perfect spots to hang refueling pods.

All of that said, at least one airliner has been modified into a fairly successful bomber.

@UnrecognizedFallingObject So much so, that airbus has done it, that's what an A330MRTT basically is.

While commercial aircraft can obviously be used for transport missions (transporting troops or military cargo) unchanged, I believe the question is really about using commercial airliners for combat missions.
I am not entirely sure if light business jets like the Learjet 35 meet the definition of a 'commercial airliner' in the question, but these civilian aircraft have been pressed into service for military missions during the Falklands war.
Learjet also make military versions of 35 series; the primary change being the addition of hard points under the wings allowing the carrying of military payloads including weapons.
Similar conversions include the older turboprop Fokker F27 conversion:
http://www.combataircraft.com/en/Military-Aircraft/Fokker/F-27-Enforcer/
So aircraft can be lightly modified to perform combat missions if they have the ability to carry external loads and some avionics to support the loads. However such aircraft would lack features found in military aircraft such as ejection seats.

Aircraft development seems to go the other way more often. Example: the Boeing 377 Stratocruiser was developed (indirectly) from the WWII B-29 bomber. It's expensive to develop a new platform; military budgets seem to be large enough for such undertakings on a frequent basis. Not so in the commercial world. Revolutionary designs like the B-707 and B-747 come along, but even they were started with military contracts in mind as much as civilian markets.

For what its worth Air Force One is operated by the United States Air Force and is built on the common 747 airframe. Although the plane is highly customized and lets be honest only servers a single military purpose it is, for what its worth a civilian plane (in a sense) that has been converted to a military function.

The title is just purpose but the detail is fighting purpose.  Military function and fighter are not the same.  AWAC and transport are not fighting purpose as in drop a bomb.   Many AWAC and transport are based commercial planes.

I understand, however one could argue that (and there is little that is really known about this) but Air Force One is rumored to have defensive and possibly attack capability.

Come on that make no sense to me and there is no physical indication of it.  If the President is on board you run and hide.

@gecko The stated question is "dropping bombs or to serve some other fighting purpose".   I even say run and hide.

The USAF's fleet of E-8C JSTARS reconnaissance aircraft were all converted from 707-300 series airliners, some of which had already seen service with a half-dozen airliners before being purchased by the USAF for conversion. Using second-hand airliners wasn't exactly cheap however, as the reported unit cost of one E-8C was still 244.4 million in 1998 US dollars (equivalent to 388.1 million in today's dollars)
As an example, here is a photo taken in 1970 of a 707-338C operated by Qantas Airlines with MSN 19622:
https://www.airliners.net/photo/Qantas/Boeing-707-338C/1467525?qsp=eJwtjUEKwjAQRe8yazetULA7PYAKeoFx8tVA0obJBFpK724I7j6Px/sbyTwZFnuuCTRSBqt86UCJlWOmcaPIU3mzWFHoA%2Bo5XEt8QavdnYa%2Br3Ke1S5rBY4NZxEkg/vzm7rmOmRp3U/96eqA3tum41C58zkFbg0Y%2B0D7/gNnqjP9
And here is that same aircraft (post-conversion) pictured 50 years later flying out of Curacao on a counter-narcotics mission:
https://www.airliners.net/photo/USA-Air-Force/Boeing-E-8C-J-Stars-707-300C/6071737?qsp=eJwtjUEKwjAQRe8yazetULA7PYAKeoFx8tVA0obJBFpK724I7j6Px/sbyTwZFnuuCTRSBqt86UCJlWOmcaPIU3mzWFHoA%2Bo5XEt8QavdnYa%2Br3Ke1S5rBY4NZxEkg/vzm7rmOmRp3U/96eqA3tum41C58zkFbg0Y%2B0D7/gNnqjP9

In the 1980s there was a proposal for a Cruise Missile Carrier Aircraft (CMCA) version of the Boeing 747, which could have carried and launched around 70-100 AGM-86 ALCM cruise missiles with nuclear warheads. This was actively considered by the USAF but rejected in favour of continuing development of the Rockwell B1 bomber.


text:
How does a fuel tank fire self-extinguish in an A380?
On Qantas Flight 32 there was...

...an undetected fire in the left inner wing fuel tank that eventually
  self-extinguished

How does a fire in a nearly full fuel tank self-extinguish?

The Australian Transportation Safety Board's Final Report gives a couple of possible reasons that the reaction was not sustained in Appendix D on page 257:

The flash fire initially consumed the oxygen inside the tank; reducing the oxygen concentration level to below the threshold required for sustained combustion of Jet A-1.
The general temperature rise associated with the initial combustion was low and insufficient to increase the temperature of the fuel inside the tank to at least the lower flammability limit of Jet A-1. Quenching of the flame by the cool fuel tank walls (evident from the sooting) and the entry of cooling air through the tank perforations may have promoted this.

Note that Jet-A requires quite a bit of activation energy to vaporize and burn. If the burning of what fuel did burn didn't produce enough energy to provide activation energy for the surrounding fuel, the fire would not be sustained. The fire was likely very brief as the turbine disc fragment passed through the tank.
From what I've heard (I haven't tried this myself,) you can drop a lit match in a bucket of Jet-A and it won't ignite. Using fuel that doesn't easily burst into flames in a vehicle designed to carry tens of thousands of gallons of fuel at several hundred miles per hour is desirable and intentional for obvious reasons.
To illustrate just how hard it is to burn Jet-A, the fuel tanks in Asiana 214 never ignited. The entire fuselage was burned out, but the fuel tanks never burned.

Remnants of Asiana 214's hull Source: Wikipedia

Jet-A from 1:50 till 3:20 https://www.youtube.com/watch?v=7nL10C7FSbE

I've not dropped a match in a bucket but I have dropped one onto fuel spread on the ground (larger surface area, more evaporation, more likely to ignite) and the match went out.


text:
When is turbulence most dangerous to an aircraft?
In what general situations or flight scenarios is turbulence most dangerous to aircraft? When could it be bad enough to bring down an aircraft (even up to something as big as an A380)?

Turbulence did not cause AF447.

The AF447 crash wasn't caused by turbulence. I'm not sure exactly what you're asking here, are you asking for a list of accidents caused by turbulence, or are you asking about general scenarios where turbulence is particularly dangerous, e.g. microbursts, wake turbulence, convective activity?

I am asking about general scenarios where turbulence is particularly dangerous, e.g. microbursts, wake turbulence, convective activity?

@anshabhi you should edit the question accordingly

Wake turbulence can affect aircraft in the most critical phases of flight such as landing approach.
For example, consider this AOPA report

On June 12, 2006, while on visual approach at Kansas City International Airport in Kansas City, Mo., the pilot of a Piper Saratoga crossed below the flight path of a Boeing 737 that was landing ahead on a parallel runway. The Saratoga encountered wake turbulence so violent that it tore apart the aircraft in flight. The pilot and his passenger were killed.

The effects are most severe for small aircraft entering the wake of a large aircraft but large aircraft can be affected too.
Skybrary lists several examples of incidents involving wake turbulance.

Turbulence is most dangerous when landing, or when it is extreme.
A sudden downdraft during landing can cause a plane to crash, notably the Dallas crash of Delta 191, in which most of the people aboard died.
Inside of storms turbulence can become so violent that it is threatening to the structural integrity of the aircraft. Although planes can and do fly inside of hurricanes and other violent storms, if the pilot makes a mistake and gives the wrong input, control surfaces can be damaged or destroyed.
Turbulence can often be quite violent near mountains, downdrafts produced by rotors and lee waves being particularly dangerous. Expert pilot Steve Fossett was killed in that way. Even large planes have been destroyed by mountain winds such as BOAC Flight 911.
Turbulence in combination with a low-visibility condition, such as a storm, can also cause a pilot to become disoriented.


text:
Why does the Antonov AN-225 not have any winglets?
Winglets provide a lift boost that would be useful to a plane of this size. But the An-255 does not have any winglets.
Why is it so?

Winglets are less efficient than a longer wing - if you cannot increase wingspan then you use winglets (or you use winglets if you want your plane to look "cool" - which is part of marketing)

Because Russian and Ukrainian aerodynamicists prefer pragmatism and don't give a s**t about marketing.

Winglets are less effective at producing added lift than an equal-length wingspan extension. They are used on airliners when simply enlarging the wing would put the plane into a larger size class, or outside the 80 m "box". A longer wingspan, which the An-225 has (10% over the limit), is better at producing lift.
The An-225 is a special purpose cargo aircraft for delivering very large loads such as the Buran space shuttle. It doesn't have to care for commercial airport traffic patterns meant for high-throughput operations - servicing thousands of planes separated into fixed size groups.
In its original role the An-225 would operate from airstrips purpose-built for it, and seeing little other traffic. Today, on the rare (or not so rare, but its most public deliveries are to remote destinations) occasion when it has a commercial airport in its itinerary, they can deal with the extra requirements of a somewhat larger plane.
Think of it like a wide load truck: they can go outside the 102"+3" limit at the expense of pre-planning the route. It's always a special delivery with these planes.

So you're saying winglets aren't to be cooler, they're to fit in airport gates.

The winglet was a way to improve the wing's efficiency without adding span either because of a dimensional limitation as Therac mentioned, or because you didn't want to add to the wing's bending by extending the tip.  A pure winglet stands straight up and all of its lift is horizontal - inboard and slightly forward.  You get a net thrust force from the forward component of the lift vector and you get an "outwash", a sideways downwash, that opposes the tip circulation. The circulation has to be strong to make it worth it and only really works on airplanes that cruise "slowly" at high altitude.

Is it really rare for An-225s to visit commercial airports? I'd have thought they'd do it almost all the time -- where else would one land? Airport terminals care about the exact wingspan of the planes because they have to park next to each other. But cargo planes don't use the passenger terminal.

Ultimately there is only one AN-225 and it doesn't fly that much (indeed it's not clear at all if it's flying at the moment, the latest evidence I could find with my google searches was from 2018). So even if all it's landings were at commercial airports they would still be a tiny tiny proportion of total landings at those airports.

@Harper Not only gates, also runways, taxiways etc.

@PeterGreen OK but surely the meaningful statistic is as a proportion of An-225 landings, not as a proportion of airport landings. One could equally say that it's rare for A380s to visit commercial airports -- only a tiny fraction of airports ever see them and, even at those airports, they're a small fraction of visits. But, if you're an A380 pilot, you land at commercial airports all the time.

@DavidRicherby I'm not really sure about the relative frequency of the An-225's visits to commercial airports vs private ones vs temporary airstrips. In any event, disruptions from handling an oversized plane don't matter so much when it's a one-off. Airliner designers, on the other hand, have to consider the impact of thousands of their planes on airport traffic.

@PeterGreen It's still flying!

Not so much a case of "still flying" as recently resumed flying. Your article describes the period as "maintenance" but other articles refer to it as a "modernization" and refers to a "domestically-designed power management and control system.". The explicit mention of "domestically designed" suggests to me that they were having issues as a result of the tensions between Russia and Ukraine.

Winglets were just beginning flight tests at NASA with a modified KC-135 when the AN-225 was designed. No one at the Antonov Design Bureau could have known at the time the benefits of using them.

Winglets have been used on corporate aircraft like the Lear 28 and Gulfstream III since the late 1970’s.  The AN-225 first flight was 1988 and could have been designed with winglets, but instead has a large wingspan which eliminates any need for winglets.

The chief designer of the AN-225 had already been working on the design for several years before he succeeded Oleg Antonov as the chief designer in 1984. Just because it first flew in 1988 doesn't mean the design could have been modified for winglets. After all, lift is not the biggest reason to use them, decreasing drag is.

@JuanJimenez The biggest reason to use winglets is to get extra lift or less drag within the same size group. If you don't care how much parking space your plane takes - and if it's the An-225, of which only a few were meant to exist, you don't care - you'll choose more wingspan every time.

I like your assumption that NASA are the only organization in the world which knows about aerodynamics :)

Counterexample: Tu-204, first flight January 1989, has winglets. https://en.wikipedia.org/wiki/Tupolev_Tu-204

@AEhere Yes, almost a decade after NASA first tested them on a modified KC-135.

The Tu-204 flew for the first time less than a month (2-01-1989) after the first flight of the An-225 (21-12-1988), so the knowledge was very much there, don't you think?

@AEhere Apples and Oranges. It didn't take a decade to design the TU-204. This speculation is pointless. I'm done here.

Well, your answer is speculative regarding what Antonov knew or not, so I guess speculation is on topic? The An-225 development ran 1984-1988, around the same years as the Tu-204 (1985-1989) according to the Russian wikipedia, so they are directly comparable: same tube-and-wings config, same country of origin, built by engineers likely educated on the same source material, etc

Winglets have been used by birds in flight for 30 million years or so (maybe more?). Homo sapien engineers were not paying attention. Winglets were first proposed in the 1800's. Also see This Month in NASA History: Winglets Helped Save an Industry.


text:
Why is this exit indicator placed here?

Some  Boeing 737s have this exit indicator in the cabin, attached in a seemingly odd position, next to the overhead bins, instead of in the middle.
Why is it placed here?

Some guesses 1) It looks like it's easier to attach the sign to the smooth curve of the roof section there than the lumpy rail right down the middle. 2) There may already be "emergency" type wiring (connected to batteries) running along that part of the roof, so not making a connection to the center of the fuselage saves weight of extra wiring.

"People who speak (assumingly) Mandarin must exit to the left, English speakers to the right"

@RonBeyer LOL! Hadn't even noticed that...

Really...?? Joke..? LOL..KKKKKK @RonBeyer

Thank you very much ;)) @FreeMan

Related, although I don't think it's a dupe

@RonBeyer It's Korean writing :)

You dont have this tagged with a jurisdiction and the answer may vary a bit by country regulations but here in the US under the FAA the requirements do not explicitly state the sign must be in the middle of the aircraft:

§ 25.812 Emergency lighting.
(b)Emergency exit signs -
(1) For airplanes that have a passenger seating configuration, excluding pilot seats, of >10 seats or more must meet the following requirements:
(i) Each passenger emergency exit locator sign required by § 25.811(d)(1) and each
  passenger emergency exit marking sign required by § 25.811(d)(2) must
  have red letters at least 1 1/2 inches high on an illuminated white
  background, and must have an area of at least 21 square inches
  excluding the letters. The lighted background-to-letter contrast must
  be at least 10:1. The letter height to stroke-width ratio may not be
  more than 7:1 nor less than 6:1. These signs must be internally
  electrically illuminated with a background brightness of at least 25
  foot-lamberts and a high-to-low background contrast no greater than
  3:1.
(ii) Each passenger emergency exit sign required by § 25.811(d)(3)
  must have red letters at least 1 1/2 inches high on a white background
  having an area of at least 21 square inches excluding the letters.
  These signs must be internally electrically illuminated or
  self-illuminated by other than electrical means and must have an
  initial brightness of at least 400 microlamberts. The colors may be
  reversed in the case of a sign that is self-illuminated by other than
  electrical means.

So if its easier due to electronic cabling, head room, brackets, or any other factor manufacturers are free to mount the sign off center.

Thank you very much for your interest!! @DAVE


text:
What is effective airflow?

As I understood, when the relative airflow meets the wing it changes, and the resulting flow is called effective airflow?

Could it signify that we are taking into account the differences in apparent relative wind direction from nose to tail or wingtip to wingtip,  caused by the airplane rotating about one or more axes?

Some context would be helpful.  There probably is no absolute defintion.

We have effective angle of attack that lies between chord of foil and effective airflow. But what is this effective airflow.

In my opinion the source ought to define it.  Is it the exact direction a smoke streamline would approach the wing, or something else?  If yes to the former then it is affected by all the things mentioned in your question and in my comment.

Looks like " relative airflow" is meant to be the undisturbed relative wind and "effective airflow" includes the upwash in front of the wing.

Hm, I would actually guess that the effective airflow takes into account the fact that the airplane is increasing in altitude. So the relative airflow is basically ground speed + wind, and relative airflow is what the airplane actually feels. I could be wrong, of course!

@Jimmy - you are right- the diagram is not compatible with my answer re upwash.  Deleting.  We need more context.  Maybe the diagram is for the left wing of a plane that is rolling to the right.  Or maybe the diagram is a horizontal stabilizer in the wing's downwash.    "I think you mean downwash instead of upwash? This may be related to the downwash produced from lifting line vortices. --Jimmy"

This is the ubiquitous picture used to (try to) explain how the downwash/tip vortices generate the additional drag component termed "induced drag". Due to the downwash/tip vortices, the actual airflow seen by the airfoil is no more at an angle $\alpha$ rather at a more inclined $\alpha_{e}$. This gives rise to a "backward inclined" lift i.e. a lift with a drag component which is the induced drag.
No need to say that the matter is actually a bit more complicated (or easier?) than this. At that link you'll also find the full picture: apparently the one that you posted has some lines deleted.


text:
One man push-back
Towbarless pushback operation of a passenger aircraft is generally done with at least 2 people. The first person (walk-out assistant) communicates with the cockpit crew members and observes the mobility on the ground, while the second person steers the pushback tractor and maneuvers the aircraft, observing the mobility on the ground. According to local airport rules or company procedures, wing tip observers may also be deployed near the wing tips.
In order to save manpower and increase productivity, it is seen that some handling companies/airlines have started to perform push-back operations with a single operator (single man push-back).
Is it safe for a single person to perform the towbarless pushback operation, both maneuvering the aircraft on the ground and communicating with the cockpit crew members and what can be the disadvantages of doing so? What kind of safety systems are these towbarless tractors equipped with?

If you're out in the open one-man towing's no big deal.  The walkers are for when you need to ensure clearance at wing tips or overhead in confined areas.

related: Why does the headset man not get on the tractor?

If the crew are inside the aircraft and sitting in the cockpit, and there are no obstacles near the aircraft, there's no problem with one person doing the push back. In the military I was certified to tow medium transport helicopters and I could initiate the tow by myself when coming from the line to the hangar if someone was in the cockpit riding the brakes, but I could not enter the hangar without walkers. Likewise, if I was going in the other direction, once I was out in the open I could tow the bird back to the line by myself.


text:
Why does the stall angle decrease as camber increases?

I have a rough idea about why $C_{{l}_{max}}$ increases with increase in camber.
But I can't explain why the stall angle decreases simultaneously.

Related (maybe duplicate since extending flaps increases camber): Why does stall speed decrease when flaps are deployed?.

You may reread your question. You can at least delete the "enter image description here"

Possible duplicate of Why does stall speed decrease when flaps are deployed?

@Bianfable I don't think that is a duplicate since flaps not only increase camber, but often chord as well; but it is definitely related.

@AEhere Yeah, I wasn't quite sure, that's why I also did not vote to close as duplicate.

At the same angle of attack, a cambered airfoil has a larger suction peak on the upper side (toward the leading edge), and a larger associated pressure recovery (toward the trailing edge).
Larger pressure recovery is equivalent to larger adverse pressure gradient, which leads to easier onset of boundary layer separation and stall.

Now, decrease aspect ratio and check the AOA curve again.  This is why the thick Gottingen airfoils of a century ago were so revolutionary, giving the slow flying, maneuvering dogfighters of that day many advantages over the thinner undercambered wing design.  Ironicly, the thinner airfoils proved superior years later as Mach numbers increased towards one.

@Robert DiGiovanni aspect ratio? I think you meant something else, there is no aspect ratio in 2D analysis.

@AEhere That's why we add the 3rd one.  Thick Hershey wings make excellent recreational airfoils, and present the other side of the spectrum from thin supercritical wings (for some strange reason I keep writing about this).

@RobertDiGiovanni the question is about airfoils, not wings, though, so bringing in the complexity of 3D flow doesn't seem like a good idea for something that can be explained in 2D.


text:
Did the airfoil choice on the P51D affect its maneuverability?
Did the wing design on the P51D, which used a laminar airfoil, affect its maneuverability? If so, how? To what extent?

Just to double check, this is about the airfoil, not the wing structural elements, right?

I wonder at the downvote; this seems legitimate at first glance, as I'd expect the stall characteristics of laminar airfoils to creep up somewhere on the edges of the flight envelope.

The choice of airfoil most certainly affects how an aircraft, any aircraft, flies -- how could it not?  Beyond that, what sort of answer are you looking for?

What my answer is no good?  The stall behaviour WAS the primary negative impact of the 1st gen laminar airfoil on the Mustang's handing.

Yes it did because the stall behaviour of the Mustang, due to the airfoil, was very abrupt and it was much easier to get into an accelerated (high speed) stall pulling high G than it was with an airplane such as a P-38, which had wonderfully benign stall behaviour and could be manhandled all over the sky in relative safety.  At the beginning of a trip in the P-51 this was made worse by the aft fuel tank's effects on CofG which made the stick forces very light so you wanted to avoid radical maneuvering until you burned off the fuselage tank fuel.
The later versions of the P-38 with hydraulic ailerons and dive flaps were just about the best propeller driven aircraft in the sky in 1944, because at high speed they could roll as fast as SE fighters and had the benefits of crazy rate of climb and no engine torque effects, on top of the very gentle stall behaviour.   One reason the Mustang dominated, even though the Lightning's technical bugs were worked out by that time, was the P-51's performance and range was great AND it was only about 2/3rds the unit cost of a P-38.


text:
How do elevons work to roll a flying wing?
I have an RC Flying Wing that uses elevons for control.  To go up both elevons move upwards and the wing pitches up. Both go down and the wing pitches down. I’m OK with this.
However, if I want to roll right, looking from the rear of the wing, the left hand elevon goes down and the right hand one goes up.  I can see this when I fly it that it rolls right but don’t understand why?
If an upward pitch angle produces lift to go up, (like when the elevons act as elevators) then why doesn’t the right wing produce more lift and thus the wing roll left? Either a flap produces lift or doesn’t?

Related: How is pitch controled in a flying wing?

I can't explain, but I was provided with some good reference books: 'Tailless Aircraft in Theory & Practice', K Nickel, M Wohlfahrt. ISBN 0 340 6142 .1; 'Only the Wing', R E Lee, ISBN 978-9-135623-03-8; 'Nurflügel', R Horten, P Sellinger, ISBN 3-900310-09-2 (In German)

Your question would only make sense if each wing was free to change its angle-of-incidence independent of the other wing, so that the elevon acted more like a trim tab than an aileron.

Good question! There's a bit of a misconception: when the elevon moves up, it actually decreases lift. It pushes air up which pushes the wing down.
This explains the roll behaviour, but how does decreasing the lift make the plane go up? The key here is that the lift is reduced only at the rear of the plane. In other words, the rear of the plane is pushed down, but only the rear. This makes the nose point up (just put the plane on the floor and push down on the tail, the nose will be up).
In this new orientation, the angle of attack (the angle of the wing relative to the airflow) is increased, and consequently the lift increases (the little bit of downforce at the rear of the wing doesn't really make a big difference). The plane will start to climb, which will reduce the angle of attack (the wing will be pointed the same way as the direction of travel), until the plane is in a steady climb.

Thank you, I know it’s simplified and aero dynamics is complicated but that’s good enough for me!

@hydev For most aerodynamic principles, you don't need complicated mathematics to understand them. The most important point is that the wings generate the majority of the lift, and the controls just point the wing (and consequently, the lift force) in a certain direction.

"and consequently the lift" - did you mean "and consequently the lift increases"?  is a word missing here?  It might also help to explain why increasing the angle of attack increases the lift.

@D.W. Yes, that's what I meant. But answering how lift works is way outside the scope of this question.

A somewhat simplified answer.
When both elevons go up, they will push the back of the plane down. This makes the nose start to point upwards, or, as we say, the plane pitches up. This increases lift, and so the plane goes up. So the sequence really is: elevons up --> back end pushed down = pitch up --> increased lift --> increasing height.
If one elevon goes up, and one down: the one going up will create a pressure downwards, the one going down will create a pressure upwards --> roll towards the elevon going up.

A downward deflected elevon creates an upward force, an upward deflected elevon creates a downward force. This pair of forces thus produce a rolling moment, making the aircraft start to roll.

"Elevons are installed on each side of the aircraft at the trailing edge of the wing. When moved in the same direction (up or down) they will cause a pitching force (nose up or nose down) to be applied to the airframe. When moved differentially, (one up, one down) they will cause a rolling force to be applied." Either a flap produces lift or it doesn’t? A little either way sure, because it messes with the wing's camber, but that's not its real job; it's a control surface to provide torque. (Everyone's taking about lift, but isn't it really: drag?)


text:
Why does a turbofan shut off when rapidly retarding the thrust levers?
In a turbofan engine, when the thrust lever is at maximum and is then suddenly pulled back to idle, the engine will shut off and lose power.
How can this be the case as the engine should be at idle when the thrust lever is brought to idle? But in this case, the engine shuts off because of the sudden movement. What is the specific reason for this?

Related: How does the FADEC prevent compressor stall during rapidly increasing thrust demand?

Related, possible duplicate: Why should jet engine throttles be moved smoothly? (answers only cover rapid increase of thrust levers, not rapidly retarding them)

I'm down voting because your question makes an assumption that isn't true, without at least pointing to the source of the misconception.

The rotational inertia of the fan will continue to push air through the engine after the fuel supply has been reduced. Reduce the fuel supply too quickly and the result is like holding a match in a gale: the wind blows the flame out.
To prevent this, modern engines use digital controls (FADEC) to ensure that the engine is kept within its operating parameters regardless of what the pilot might do with the throttle.

This was only a problem on the 1st generation of turbojets, where the fuel controller was effectively a needle valve controlled by the thrust lever and the "fuel control" was the pilot's brain.  These engines also had the reverse problem; you couldn't "slam accelerate" them without overtemping and/or flaming out.
Once hydromechanical fuel controllers came about in the early 50s you could move the thrust lever all you wanted (within reason) because the lever provided a mechanical "command" and the fuel controller actually managed fuel flow based on continously measured engine parameters to achieve the commanded setting.
The next step from that was electronically trimmed hydromech fuel controllers in the 70s, then FADEC in the 90s.  But it was only in the 40s and early 50s that you had to carefully move the thrust lever to that degree.


text:
Are low wings less safe for aerobatics training?
I fly a low wing (CZAW SportCruiser) and am looking for aerobatics training schools, however I can only find schools with high wings available for training. My plane has "no aerobatics" placards inside the cockpit, so apparently I can't use my own plane. Are low-wing aircraft less safe for aerobatics training?

Aerobatic specials are low-wing (Zlín Z-50) to mid-wing (Zivko Edge 540; Extra 300 is somewhere between). I can't think of any high-wing one. But there is a couple of common high-wing aerobatic-capable trainers, which is what the schools use.

No.
It has nothing to do with the configuration, but the structure, the engine and the fuel system of your aircraft. The SportCruiser is certified in the Light Sport Aircraft (LSA) category and is meant for flying right-side-up. For aerobatics, you need

a fuel system than can still feed the engine when the load factor is less than or equal to zero,
an engine which can still lubricate all moving parts when it is experiencing a negative load factor, and
a structure which can tolerate higher load factors than what you can expect from cruising along at 115 kts max in fair weather.

The wing location has no impact on aerobatic fitness. You might even argue that the unrestricted view up in a low wing aircraft helps to see better what is ahead in steep turns.

I'm not trying to do aerobatics in the sportcruiser, but knowing how to fly an aircraft to the extent of its flight controls I'm told by several of my instructors could one day save my life

@boulder_ruby: I fully agree. I would even go further and would recommend to train spins in the cruiser once you have some experience and have gone through the exercise with an instructor.

@boulder_ruby That's a sensible objective, but it's hard to learn fly a plane to the limit of its performance envelope, until you have learned to recognize when you might exceed that envelope, and how to recover if you do exceed it. A drill like intentionally entering and recovering from a spin is not just about doing the right things with the controls - it's also about training your mental ability to get into and out of a potentially fatal situation without losing your personal self-control! You don't want to start by adding "fear of breaking your own aircraft" to the training scenario.

Well, here's the thing.  Technically any type of airplane is CAPABLE of aerobatic flight to a certain degree, even normal or utility category aircraft, as this demo by Sean Tucker in a Cessna Corvalis TT.

Bob Hoover famously flew his air show routines in a Rockwell Shrike Commander.

And Boeing test pilot Tex Johnson famously rolled a 707 - twice - in front of Boeing execs and Pan Am representatives during SeaFair.  He was very nearly fired personally by William Allen for the stunt.

None of these aircraft mentioned are approved for aerobatic maneuvers, yet can cexcute certain ones in the hands of a skilled pilot who keeps the airplane flying within the load factor limits of the structure, engines, and systems.
As mentioned above by Peter, aircraft that routinely fly aerobatic maneuvers are approved to do so by the manufacturer after a rigorous flight test schedule which include carefully approach the design limits in meticulously planned test points and having multiple backups in the event of an emergency i.e., parachutes, spin recovery chute canisters, etc.
Low wing or high wing really has minimal effect on how good of an aerobatic airplane it is, though most dedicated aerobatic platforms and military fighters use a shoulder mounted wing for neutral roll stability.
And even then an aerobatic aircraft is only approved for certain maneuvers fully demonstrated during flight test and only when operated in the aerobatic category (they are often certified in both normal and aerobatic categories).  A Bellanca Super Decathlon, for instance, is prohibited from doing aerobatics when loaded in the normal category CG range; in the aerobatic CG range, it is prohibited from doing tailslides and Lomcevaks .
A sport cruiser, while designed to fly straight and level can be put through a benign aerobatic maneuver like an 1G aileron or a barrel roll and do just fine.  However you have to know what you're doing with the plane first;  if you don't you're inviting disaster.  Aviation is full of seemingly benign situations which quickly turn into death traps when approached by the negligent, the incompetent and the neophyte.  Aerobatic flight does not require a license, rating or instructor sign off to attempt largely because the participants have s lot of respect for the capabilities of the aircraft, know their limits and seek qualified instruction first.  Let's keep it that way.
Bottom line is if you don't want to fly with the pointy end forward and the dirty side down, do so in an aircraft specifically designed to do so, operate it within the OEM's published limits, and obtain instruction from a competent source.


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How does an aft CG affect Vmcg?
How does an aft center of gravity affect the minimum control speed on ground (Vmcg)? Does it reduce all V-speeds?

By changing the load on the nose wheel. More forward cg position requires less rudder for lateral control.

This document from Airbus says that VMCg depends mainly on engine thrust and pressure altitude. No mention of CG.

@RyanBurnette: The document also says that steering is not used in certification. But it continues "steering would be helpful in controlling the aircraft". And steering clearly works better with more load on the nose wheel.

$V_{mcg}$ is the minimum speed on the ground at which control is possible using rudder alone upon failure of critical engine. From FAR Part § 25.149:

VMCG is the minimum control speed on the ground, and is the calibrated airspeed during the takeoff run at which, when the critical engine is suddenly made inoperative, it is possible to maintain control of the airplane using the rudder control alone (without the use of nosewheel steering), as limited by 150 pounds of force, and using the lateral control to the extent of keeping the wings level to enable the takeoff to be safely continued.

As the center of gravity moves forward, the rudder arm increases, improving rudder effectiveness. As a result a forward cg results in a lower $V_{mcg}$. This is the reason the tests for $V_{mcg}$  is carried out at the rear most possible center of gravity. From Advisory Circular 23-8C: Flight Test Guide for Certification of Part 23 Airplanes:

For rudder limited airplanes with constant aft c.g. limits, the critical loading for VMC testing is most aft c.g. and minimum weight.  Aft c.g. provides the shortest moment arm relative to the rudder thus the least restoring moments with regard to maintaining directional control.

as,

There are variable factors affecting the minimum control speed.  Because of this, VMC should represent the highest minimum airspeed normally expected in service.

Wrong, on the ground the airplane does not pivot around the cg.

@PeterKämpf, and neither does it in the air, right? Because a torque is caused by pair of forces and the arm between them is what determines the torque and CoG only matters as action point of inertial forces (including gravity). But it this case all the forces are aerodynamic.


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Where does the Olive Branch (KOLV) class D ceiling meet the Memphis (KMEM) class B floor?

I'm having an internal debate on interpreting the Class D ceiling in part of the the Memphis TAC. My understanding was in the case of a Class D under a Class B shelf, the ceiling of the Class D ends at the floor of the Bravo, or in this case: 1,800ft MSL.
However, the [29] box printed inside the area of the Class B/D is causing  confusion. Is this explicitly stating the Class D does extend to 2,900ft MSL or does it end at 1,800ft MSL as I originally thought?

As has been noted in a comment, this question could use some clarification to indicate that you are only asking about the part of the Class D airspace that is charted as appearing to underlie a Class B shelf with a 1800' MSL floor (if you are).  However, I see you have not been active on ASE since this question was posted, so...

PS I think the fact that they chose to put the boxed "29" numeral in the western part of the Class D airspace rather than the eastern part is of no consequence whatsoever.


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At a constant power setting, does TAS change with altitude?
I found a lot of references to the question but no definite simple answer.
What would be the influence on true airspeed (TAS) for same airplane at same throttle setting flying straight and level at higher altitude?
Would it change for Jet engine vs internal combustion engine?

Jet is also an internal combustion engines. The four kinds of engines are: jet, turboprop, turbo-charged piston engine and normally-aspirated piston engine. Each behaves somewhat differently.

The "Same throttle setting" bit actually complicates this question because that isn't how airplanes are typically operated so finding data is hard.  A better question would probably be, "does TAS change with altitude at a constant IAS".

@Lnafziger: That “better” question is trivial and almost surely already answered, because it takes the engine out of the question.

Do you mean constant power setting or constant throttle setting? these are different in an airplane

The answer to your question largely depends on what you mean by "constant throttle setting".
For propeller propulsion, if "constant throttle setting" means "constant power setting" as in a fixed output BHP, TAS will increase almost linearly with altitude (up to the altitude where constant power output can no longer be maintained).
For a normally aspirated reciprocating engine with a fixed pitch propeller, a constant throttle position will mean a decreased manifold pressure with increased altitude resulting in less power output, less thrust (T), and thus decreasing TAS (assuming the decrease in thrust is larger than the decrease in drag (D) resulting from the decreased density at higher altitude, this generally holds true). For a supercharged engine, depending on how the supercharger is controlled, "constant throttle setting" can have the charge control maintain a constant manifold pressure. In this case, the power setting will be maintained (up to the maximum altitude where the supercharger can maintain the manifold pressure), and TAS will increase.
For a jet propulsion engine, once again it depends on what is implied with "constant thrust setting". For example, for low/no bypass engines, a constant EPR should roughly correspond to constant T with altitude, hence with D decreasing with altitude, TAS will be higher before T = D. If "constant thrust" means "constant N1", thrust will actually decrease with altitude, how quickly it decreases with altitude will determine the effect on TAS (once again, where T = D).
If "constant throttle setting" simply implies "constant thrust". Resulting TAS will always be higher (as for a given TAS, T remains constant and D once again decreases).

"constant power setting" means a certain percentage of rated engine power, eg "75% power," which could mean different throttle, prop, mixture settings at different altitudes

rbp, thank you, it was a long time ago since I've been dealing with propeller propulsion, I've edited my reply accordingly.

@rbp: I suspect the intention of the question is exactly opposite. "constant power setting" means the throttle, prop and mixture levers (resp. power and prop levers resp. thrust levers) are at the same position.

good point. i'll ask.

The true airspeed (TAS) is determined by adjusting the indicated airpseed (IAS) for altitude and outside air temperature (OAT).
Faster small airplanes have a TAS calculator built in to the ASI. To use it, the pilot dials in the pressure altitude read off the altimeter (ALT), and sometimes the OAT, and reads the TAS off a separate dial on the ASI. In this photo, the IAS is 105kts, and the TAS is 129kts @14,000ft, 147kts at 16,000, 164kts @ 18,000ft, 182kts @ 20,000.
In one airplane I fly, the cruise setting is 34" MP and 2400 RPM. This setting produces a higher TAS at higher altitudes.

For airplanes that don't have such a dial, the pilot can estimate the TAS by adding 2% per 1,000ft of altitude to the IAS. For example, 100kts IAS at 10,000 ft pressure altitude is 100kts * 20% = 20kts. So the TAS would be 120 kts.
True airspeed calculations become less accurate as altitude increases and the planes flies faster, but a jet and a plane both flying at the same indicated airspeed at 10,000ft will read the same TAS off the dial.
At higher altitudes, jets and turboprops use an "air data computer," such as this one, which states:

Air data computers are used by aircraft to acquire and process data
  from sensors (such as pitot tubes and avionics buses) to obtain key
  air data parameters such as altitude, airspeed, height deviation and
  temperature to ensure safe and accurate flight detail, on both rotary
  and fixed wing aircraft.


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What is the average temperature in the luggage hold of a passenger plane?
I am asking this seemingly odd question, as we'll have to transport some medicine in our luggage and it's supposed to be stored at temperatures between -8C and +2C. I'm not sure, if airport security will allow this to pass if this is in a cooling box as hand-luggage, although, in my opinion there shouldn't be a problem, as the ampules are 4 x 1 ml and I have a prescription (however, the cooling box will probably be treated as partially liquid containing).
Your advice will be much appreciated!

Have you considered asking the airline? The temperature is not likely to be the major issue. That being said, I suspect the temperature is close to cabin temperature.

the TSA allows you to bring medicine in your carry on luggage, including ice packs to keep them at temperature.

I believe this question is better on Travel.SE

I am inclined towards this being related to aviation as it talks about something related airplanes. Although this question has already been asked.

@erich The asker's profile gives their location as the UK and the question doesn't mention travelling to the US. As such, there's no indication that what the TSA allows is in any way relevant.

If you look at the actual question here - what is the typical temperature in the luggage hold of an airliner? - then I think this is indeed on-topic and can be clearly answered. Everything about the TSA, security, liquids, country of travel etc. is actually irrelevant to the basic point about temperature.

I'm voting to close this question as off-topic because it has been asked on Travel.SE.

Thanks for all the comments and for pointing me in the right direction!

According to an A320 pilot quoted in this question on travel.SE (and see this one too), the temperature can be 7C at the low end but potentially above 18C if animals are being transported. Therefore, if you want to transport something in the hold that needs to be kept at a specific temperature range you would need to check with the airline about how to do that.


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How can wingtip vortices affect the direction of the relative wind in front of the leading edge?
I have a question on aeroalia's answer on this post (Why does the vortex created by wing affects its own angle of attack?).
If I'm not mistaken, wingtip vortices are generated behind the trailing edges of the wings and, even if we assume wingtip vortices somehow can reach the front area of the wings, it would only be able to affect the relative wind in front of the leading edge on the far outboard of the wings close to the wingtips, because after all it's wingtip vortices. Then, how could it be said that the upwash from the wingtip vortices changes the direction of the entire relative wind?

Please don't believe everything you read. You healthy scepticism is your best defense against the nonsense you might read about wingtip vortices.
What causes the flow to increase its angle when approaching the leading edge is the low pressure region above the wing. This is not only the main contributor to the wing's lift, but also the reason for the flow pattern ahead of the wing, in combination with the overpressure region around the stagnation point.
Please read this answer and let me know if something is left unclear.

Kampf So from the first link, I understand that wingtip vortices are actually the product from the entire trailing edge of the wing, not just from the wingtip. But I still don't get that how the low pressure above the wings works to push up the angle of the relative wind ahead of the leading edge. Even in an image given in your second link, the inflowing impulse stays horizontal while the outflowing impulse bends downward.

@lemonincider: The suction above the wing works like the nozzle of a giant vacuum cleaner - why should it not suck in air from ahead and below?

If that's the case, I mean, if the air ahead of the leading edge is sucked by vaccuum on the upper surface of the airfoil, shouldn't the relative wind ahead of the leading edge curve upward into and along the leading edge, not downward as described in this picture of the effective relative wind (https://en.wikipedia.org/wiki/Lift-induced_drag#/media/File:Induce_drag_downwash.png)?

@lemonincider Yes, it does. Don't look at silly graphics, better use real flow visualisation, like that classic here. There are even websites which explain things correctly.

After reading the website you suggested, I studied the graphic harder and realized it's not really the depiction of the effective airflow ahead of the leading edge; it's just an extension of the effective relative wind behind the trailing edge. Thank you.

@lemonincider: The graphic is still bunk. The resulting lift vector is not perpendicular to the downwash direction but to the mean between free flow direction and downwash.


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How do different RPM–MAP settings affect range?

For a cruise in constant-speed prop aircraft, you can choose different combinations of the manifold pressure and prop rpm to generate the same amount of power. For example, in order to generate 117 BHP (65% Rated Power) at sea level in the chart above, you can select either the combination of 24.5 for MAP and 2100 for rpm or that of 22.9 for MAP and 2400 for rpm. Here, what's the difference (if any) in selecting different combinations of rmp and MAP to generate the same power? Any benefits using the combination of low rpm and high MAP or vice versa?
This other post answers my original question, yet I have a follow-up question:

How does the combination of low rpm and high MAP extend the flight range?

To my knowledge, whatever combinations are chosen, as long as the combinations generate the same power, the same amount of fuel is consumed. The above chart supports that: The same 10.3 Gal/Hr is flowed into the engine regardless of the combinations in the box.
For your information, I asked the same question to my instructor, and he told me there's really no difference when it comes to power and fuel efficiency. But I was not persuaded at first, because I thought it was the MAP that controlled power output (BHP), and therefore, the less the MAP, the less fuel required. And a more efficient use of props could supplement this loss of power, resulting in the same thrust power. But the above chart just contradicts my reasoning. According to the chart, it's not the MAP alone but the combination of MAP and rpm that determines the BHP. But if it's the case, I don't understand how the range of flight could be extended by decreasing MAP and increasing rpm.

Does Skip Miller's answer to this question not cover it well enough for you?

@UnrecognizedFallingObject Looks like Skip Miller's answer covers my question. I'll edit my question. Thanks

@RalphJ I edited my question.

Some things to consider:
1) Engine Frictional Losses tend to be lower when turning slower for the same power output. (less sliding and rolling, less oil splash on the crank, less pumping loss from air in the crankcase)
2) Big engines turning slowly at wide open throttle tend to be more efficient. It is easier to draw in the air slower through a wide open throttle (WOT) than turning faster at partial throttle.
3) Propeller Efficiency changes with prop speed, pitch, and airspeed.
Not giving you a definitive answer, but, for a given airspeed, there will be an efficiency peak that is determined by the points above.

Thanks. By your last comment, do you mean it's not necessarily the combination of the highest MAP and the lowest rmp (for the same power output) that brings the greatest efficiency?


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Why is mid point RVR given?
I cannot understand why mid point RVR is issued and what's the significance of it

Closely related

It is (or was - I'm not sure) relevant because it is limiting:

The touch-down zone RVR is always controlling. If reported and relevant, the mid point and stop end RVR are also
controlling. The minimum RVR value for the mid-point is 125 m or the RVR required for the touch-down zone if less,
and 75 m for the stop-end. For aeroplanes equipped with a roll-out guidance or control system, the minimum RVR
value for the mid-point is 75 m.
Note: “Relevant”, in this context, means that part of the runway used during the high speed phase of the landing down to a speed of
approximately 60 knots.

source: JAR-OPS 1.405 - 1.0.5 (f)
The significance, I suspect, is because it's useful to be able to see where you are going when moving at high speed along the mid section of the runway and in manual control of steering.

Yep, as you thought, one might still be going quite fast after the touchdown zone. It is totally possible to have huge differences in visibility over a very short distance, and the area of poor visibility just might be right after the touch-down zone. You don't want to plow into a wall of thick fog doing 130kts. It is just as easy to lose sense of direction and or place on ground as it is in the air, even if you have runway lights to guide you. Then there' the elevated risk of collision, of course, should a runway incursion occur.

Thank you for the answer


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What are the amber triangles on the ECAM bleed page on an A320?
In FCOM they say that triangle becomes amber when RAM AIR flap is not fully open, and both pack flow control valves are closed.
Here the RAM air flap is emergency ram air or RAM Air flap for the Packs?

It refers to the valve controlled by the guarded RAM AIR pushbutton referred to as "emergency RAM air" in the system diagram.
When the triangles (think of them as arrows indicating flow) are white the triangles indicate sufficient flow of air for conditioning/pressurisation.
The normal position of the guarded Ram Air pushbutton is 'off', ie no light illuminated.
In case both packs fail/shutdown, i.e. both the pack valves are closed, the remaining source for getting airflow through this system is the RAM air. If that is not fully open, while the pack valves are both closed there is insufficient airflow and the triangles therefore turn amber.


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What is the difference between MMEL and MEL?
What was the need to introduced MEL if MMEL is there and is less restrictive than MEL ?

The Master Minimum Equipment List is issued by the manufacturer with the approval of the regulator and can be considered a "global" document you might say.  The manufacturer will work hard to build the mathematical case to make the requirements as broad and flexible as it can. It's an ongoing process, and as the type is introduced and matures, the OEM will continue to increase the scope of the MMEL, because each new item added improves Dispatch Reliability (because more more and more components and subsystems can be inop without needing to be fixed right away).
The MMEL is the foundation for the Minimum Equipment List that the airline uses.  The MEL is an in-house document created by the airline and approved by the local authority.  It'll be based on the MMEL but may have additional limitations imposed by the local authority as it deems necessary for that operation.
It's similar to the Maintenance Program. The OEM will issue a Maintenance Program for a given aircraft type, but each airline will have its own variations by negotiation with its local authority.

The airline can also opt to not include some items in MEL if it considers ability to dispatch with them inoperative isn't worth the additional procedures it would have to define and train for that case, no?

Possible theoretically, but I can't think of a case where an airline would do that. Since items are added to the MMEL to improve dispatch reliability by allowing dispatch with inoperative items, by definition the inclusion of an item means there is a net benefit to deferring an inoperative component.  The alternative is a delay or cancellation, and I've never seen a case where that is preferable to an "M" procedure (deactivation by techs) or an "O" procedure (flight crew mitigating action).  Each plane will normally have a box full of deactivation parts like blanking plates in the cargo compt.

The MMEL should list every piece of equipment and systems with which the aircraft was originally certified. It may place each piece of equipment into the category of being necessary for specific operations. This designates whether an aircraft continues to be airworthy and meets the standards of its Type Certification.
The MEL is a list of equipment that is allowed to be inoperative and the aircraft still be considered airworthy by the operators. While the MMEL is created by the manufacturer in conjunction with the civil aviation authority responsible for type certification and airworthiness standards and determination. The MEL is created by the owner/operators of the aircraft using the MMEL and heir own SOPs as a starting point.


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What is the full-form of ATA?
I was going through FCOM of A320 and came to know that FCOM chapters are called as ATAs. So first of all what is its full- form and secondly why do we call the chapters ATAs ?

ATA stands for Air Transport Association (today called Airlines for America). The numbering standard is called ATA 100 and was widely used for various types of aviation documents and manuals from 1956 until 2015 according to Wikipedia:

ATA 100 contains the reference to the ATA numbering system which is a common referencing standard for commercial aircraft documentation. This commonality permits greater ease of learning and understanding for pilots, aircraft maintenance technicians, and engineers alike. The standard numbering system was published by the Air Transport Association on June 1, 1956. While the ATA 100 numbering system has been superseded, it continued to be widely used until it went out of date back in 2015, especially in documentation for general aviation aircraft, on aircraft Fault Messages (for Post Flight Troubleshooting and Repair) and the electronic and printed manuals.

The basic function of ATA 100 was a system to categorize systems, subsystems and sub-subsystems etc, to a universal standard. This allows the same numbering convention to be applied across documentation where they follow the ATA 100 standard.  This can extend down to an OEM's engineering drawing system, as well as internal and external documentation.
So for Flight Controls, with the assigned ATA100 number of Chapter 27, you know that Maintenance Manual sections, Parts Manual section, FCOM sections, Service Bulletins, OEM internal work documentation, pretty much anything connected to flight control systems, can be found the indexing system at Chapter 27, or some number prefixed with 27.
I worked at an OEM that didn't use ATA100 for its engineering drawing system, so it's drawings were categorized under some other convention.  If you wanted to search for a Flight Controls drawing, you had to look up an index to find where to look because the numbering was something someone made up.  It was quite a pain until you memorized that particular drawing system.
For an ATA100 compliant drawing system, if you were already familiar with ATA 100, you knew that flight controls drawings would all start with 27 as the first 2 digits of the drawing number, and subsequent numbers would also follow the ATA100 sub-system convention. It makes things much easier to find and you knew where to look in any manual or document of any OEM that follows the standard.


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Why was NWS shifted from green hydraulic to yellow hydraulic system in the A320?
In older Airbus A320s, the NWS (nose wheel steering) was on the green hydraulic system and now it's on yellow. What's the reason for the change?


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What is the difference between boomset and headset?
Both "boomset" and "headset" are terms used e.g. by Airbus:

The audio management system includes:

[...] sockets at each station

headset jack and boomset connector (hand microphone connector) for pilot, copilot and third occupant
headset jack for fourth occupant

[...] boomsets for the pilot, copilot, and third occupant, and three hand microphones (fourth) [...]

(Airbus A320 FCOM - Communications - General - Audio Management System, emphasis mine)
What's the main difference between these two things or are they the same?

Can you give us the context and where you heard "boomset"?  Because I have never heard this word used...

@Biafable, thanks. That's just the sort of reference and contextual information I would expect an OP to include in a "good" question. Hence my comment. (BTW, the term is found on the eighth page of the PDF file - which is labeled Page 1 of the Comm section in the document itself.  In case it saves anyone else hunting around...)

I'm not sure about this context, but a boomset may be a mic/headphone combo that covers a single ear (like you would see phone operators wearing), whereas headset covers both.

Or even, just a boom mic... listen to the speaker, push to transmit on the yoke, voice picked up with a boom mic. Dunno, as I'd never come across the term before either, but I'll offer this as a guess.

@RonBeyer that was my guess.

"Shake your boomset" does not mean to lift up your headset in your hand and give it a shake--


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What is the relation between N1 and Wing anti-ice
When wing anti-ice is selected, the N1 or EPR limit is automatically reduced, and the idle N1 or EPR is automatically increased. What does this statement mean ???

I understand about descent but what about in flight cruise

When engine or wing anti-ice are needed, the required amount of bleed air increases. In order to provide enough bleed air at the required pressure, the engine idle speed must be increased. That way, the compressor runs faster, which provides more high pressure air to the bleed valves. Note that this will result in more idle thrust as well, which can have an impact on descent performance as discussed for the Boeing 737 here: What is the impact of thermal Anti-Ice on descent performance?
For the A320, this is already taken into account for the descent calculation:

The idle segment assumes a given managed speed flown with idle thrust plus a small
amount of thrust. This gives some flexibility to keep the aircraft on the descent path if
engine anti-ice is used or if winds vary.

(Airbus A320 FCTM - Normal Operations - Descent)
When more bleed air is taken out of the compressor stage of the engine, the EGT (exhaust gas temperature) will increase because more fuel flow is required to maintain the same N1 speed. This implies that the N1 or EPR limits must be decreased in order to protect the engine, meaning the lower limit will result in the same EGT as before.

When more bleed is taken out, the fuel control system has to schedule more fuel to the combustor to ensure the same level of performance (i.e. thrust) is maintained, not because of less air reaches the combustion chamber (that will not happen). An engine with increased bleed extraction or increased power (electrical, for electric anti-ice systems) off-take results in an increased EGT and increased spool speed of scheduling extra fuel, this will reduce the margin to the max allowable EGT.

@0scar You're right, thanks for the comment. I updated the answer. Feel free to edit if it's not quite right yet.


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What is the difference between LP fuel valve and LP fuel shut off valve?
In the Airbus A320 FCOM in some places "LP fuel valve" is mentioned (in Fire and Fuel System chapters) whereas in the engine chapter "LP fuel Shut off valve" is mentioned.
Is there any difference between the two?

The "LP fuel valve" and "LP fuel Shut off valve" are the same valve just being named differently in different sections of the FCOM.
The valve is located in the wing leading edge and is also sometimes referred to as “spar valve” by engineers who also work on Boeing aircraft.

Somebody in the Airbus Pubs department isn't following Airbus's Nomenclature standard.

They are the same valve.
The engine has two fuel (shut off) valves:

LP valve: This valve is located in the leading edge of the wing and can stop any fuel flowing towards the engine through the pylon. When it is closed (e.g. by the fire handle), the entire engine with all of its systems is starved of fuel.
HP valve: This valve is located deep within the actual engine. It controls the fuel going to the combustion chamber. It is opened by the FADEC during normal engine start. But even when it is closed, the engine still receives fuel for all the other systems (see diagram below).

This is the engine fuel diagram from the FCOM:

(Airbus A320 FCOM - Power Plant - Fuel System)
As you can see, the LP valve is right at the beginning of the fuel flow diagram. The cold fuel is used for cooling the engine oil (fuel oil heat exchanger and servo fuel heater) and the Integrated Drive Generator (IDG oil cooling). It is also used for hydraulic control. The HP valve is shown at the bottom before the fuel metering unit and the engine fuel nozzles.